) The goal of this research program is the development of new drugs for the treatment of resistant diseases. Although adriamycin (doxorubicin) and other anthracycline drugs are valuable chemotherapeutic agents, a major problem associated with their use is specific and multi-drug resistance. This study will explore the mechanism of drug cytotoxicity in both sensitive and resistant human breast cancer cells, with and without treatment by doxorubicin, daunorubicin, and epidoxorubicin. Preliminary studies indicate that formaldehyde plays a critical role in this mechanism, and that newly synthesized anthracycline-formaldehyde conjugates exhibit greatly enhanced cytotoxicity toward resistant cells. In addition, serious side effects associated with anthracycline drugs, including cardiotoxicity and myelosuppression, may be reduced since the intracellular redox chemistry which produces formaldehyde is now unnecessary. The chemistry, differential cytotoxicity and delivery of these new drugs, Doxoform, Daunoform, and Epidoxoform, will be fully characterized. The studies will be extended to both sensitive and resistant human prostate cancer cells to explore the generality of the drug applicability and mechanism. The aminoglycoside antibiotics such as gentamycin, tobramycin, neomycin, and amikacin will also be examined in conjunction with resistant and sensitive strains of E. coli to determine whether similar mechanisms of cytotoxicity are operative. This research will employ chemical ionization mass spectrometry in a tandem flowing afterglow-selected ion flow tube for the quantitative characterization of formaldehyde and catalytically related species in sensitive and resistant cells, with or without treatment of both conventional drugs and drug-formaldehyde conjugates. These studies will be complemented by confocal microscopy, HPLC, flow cytometry, UV/Visible spectroscopy, NMR, and electrospray mass spectrometry for a full characterization of these systems. The drug effectiveness (IC50) will be interpreted in terms of the intracellular chemistry, drug delivery, and the nature of the drug-DNA adducts as revealed by all these techniques, with the aim of developing even more effective drugs against resistant diseases.